“Surprisingly, some of those shunts were quite large,” Spence said — about one-quarter of the missed defects were in the three highest grades of severity, according to a five-grade measure.
Accurately detecting PFOs, and knowing its grade, can help doctors decide whether a stroke was due to a paradoxical embolism, Spence said. Other clues related to the patient’s stroke are also helpful, including shortness of breath at stroke onset; sitting for a long time, such as on an airplane; waking up with a stroke; and having a history of migraine, sleep apnea, deep vein thrombosis, varicose veins or pulmonary embolism.
Diagnosing the underlying cause of a stroke is essential to choosing the right medicine to help prevent future strokes, Spence said. Anticoagulant drugs are three times more effective than another commonly used class of drugs, known as antiplatelet agents, in preventing the type of stroke that can be caused by a clot passing through a PFO, he said.
The study’s findings may also be important in understanding which patients with PFO might benefit from closing the hole surgically or with a catheter-deployed device. PFO is present in about one-quarter of the population but accounts for only about 5.5 percent of strokes caused by paradoxical embolism. This suggests the defect isn’t a problem in about 80 percent of patients with it, Spence said. “That’s why these clinical clues are so important,” he said.
Compared with echocardiography, the cost of transcranial doppler equipment is about one-fifth that of a modern echocardiogram machine; heavy sedation is not used as it typically is with transesophageal echocardiogram; and transcranial Doppler is helpful for other purposes, such as learning which patients with asymptomatic narrowing of the carotid artery may warrant surgery. “More stroke centers should be doing transcranial Doppler,” Spence said.